Let's talk about genre, if you want to write a simple lead sheet, you'll
be up and running fairly quickly. But, you'll have to put in the work, and
you'll have to understand the concepts involved. You will be able to teach
yourself, if you like, or you can get help. If you want to write piano-vocal
music, and you're not intimitely familiar with the instruments involved
(voice and piano) you have a bit more work ahead of you. And whoah! If you're
interested in arrangements or orchestral works, or more "complex"
pieces with lots of instruments...well, then you're in it, as I am, for
the "full-meal deal" as a composer.